Seasonal and annual variation in transpiration of a dominant desert species, Haloxylon ammodendron, in Central Asia up-scaled from sap flow measurement

Abstract

Transpiration in plants is a critical eco-hydrological process linking plant-atmosphere interactions and is very important in the arid environment because the surface runoff is of no practical importance in terms of the hydrological budget. Investigations on transpiration in arid land species under natural conditions have not been comprehensive, however. We present here the long-term transpiration of Haloxylon ammodendron, a dominant species growing at the southern edge of the Gurbantünggüt Desert, China, during the growing seasons from 2009 to 2011 using up-scaled sap flow monitoring with the thermal dissipation probe method. The sap flux density averaged 1·86m3m-2day-1 during the measurement period for 3years, and the transpiration per day based on ground area (EC) ranged from 0·05 to 0·27mmday-1 and averaged 0·14mmday-1, lower than that of other species largely because of the extremely arid environment. The canopy stomatal conductance averaged 16·75mmolm-2s-1 and maintained a constant low value under high vapour pressure deficit, which is essential for maintaining low transpiration compared with other species. High seasonal variation in EC was exhibited because of the plant's response to environmental factors at seasonal scale. EC showed much less variability at annual scale, however, because of the constant balance between the evaporative demand of the atmosphere and plant factors. These results contribute to a better understanding of the plant's transpiration in arid land and its response and adaptation to climatic changes at annual and seasonal scales.